Polyethylene Composition Suitable for the Preparation of Films and Process for Preparing the Same

ABSTRACT

A polyethylene composition, in particular suitable for the preparation of films, and a process for preparing the same are described. The polyethylene composition of the invention comprises from 50 to 89% by weight of a first polyethylene component comprising at least one multimodal polyethylene including a plurality of ethylene polymer fractions having distinct molecular weights and comonomer contents, at least one of said plurality of ethylene polymer fractions being prepared by the use of a single site catalyst, and from 50 to 11% by weight of a second polyethylene component comprising a low or medium density polyethylene.

FIELD OF THE INVENTION

The present invention relates to a novel polyethylene composition, to aprocess for the preparation thereof, as well as to a film comprisingsuch a polyethylene composition.

In the field of preparation of polyethylene films, particularly in thefield of medium density (MDPE) and high density (HDPE) films, there is along-felt need of providing films having, at the same time, a number ofmechanical and physical properties, and in particular adequatemechanical strength, processability and transparency, which are normallyconflicting with each other.

In the present description and in the following claims, the expression“medium density film” is used to indicate a film having a densityranging from above 0.930 to 0.940 g/cm³, while the expression “highdensity film” is used to indicate a film having a density above 0.940g/cm³.

In polyethylene film applications, a possible way to evaluate theabove-mentioned properties may be made through the following parameterswhich, in the present description and in the following claims, aredefined and determined as specified hereinbelow.

The mechanical strength of a polyethylene film may be effectivelyevaluated, for example, by means of the dart drop impact, which gives ameasure of the puncture resistance of a film under shock loading. In thepresent description and in the following claims, the dart drop will bereferred to as determined by ASTM D 1709, Method A.

The processability of the composition on which the polyethylene film isbased may be determined in terms of MFR according to standard ISO 1133,condition G, corresponding to a measurement performed at a temperatureof 190° C. and under a weight of 21.6 kg.

The transparency of a polyethylene film may be expressed in terms ofhaze, gloss and/or of clarity. In the present description and in thefollowing claims, the haze will be referred to as determined by ASTM D1003-00 on a BYK Gardener Haze Guard Plus Device on at least 5 pieces of10×10 cm film, while the gloss will be referred to as determined by ISO2813 and the clarity will be referred to as determined by ASTM D 1746-03on a BYK Gardener Haze Guard Plus Device, calibrated with calibrationcell 77.5, on at least 5 pieces of film 10×10 cm.

In the field of films, the above-mentioned mechanical and opticalparameters should range in ranges meeting the requirements set by thepackaging industry in the production, for example, of hygiene films andlaminating films for food packaging, where transparency should be ashigh as possible.

PRIOR ART

Several polyethylene films are known whose properties essentiallydepend, in addition to on the nature of the composition on which thefilms are based, also on the way in which the film is prepared and, inparticular, on the kind of process used to prepare the same. Among thedifferent steps used to carry out the process, a key role is played bythe catalyst system selected in the (co)polymerization step(s) which arecarried out to obtain the polyethylene starting from ethylene and,optionally, one comonomer or more comonomers.

Accordingly, in the present description and in the following claims, theterm “polymer” is used to indicate both a homopolymer, i.e. a polymercomprising repeating monomeric units derived from equal species ofmonomers, and a copolymer, i.e. a polymer comprising repeating monomericunits derived from at least two different species of monomers, in whichcase reference will be made to a binary copolymer, to a terpolymer, etc.depending on the number of different species of monomers used.

Among the prior art medium density polyethylene films, films prepared bymeans of chromium catalysts are known. Although substantially suitablefor the purpose, the polyethylene films based on chromium catalystssuffer from an insufficient mechanical strength and a very poortransparency. By way of illustrative example, the known polyethylenefilms prepared by means of a chromium catalyst have a dart drop impactranging from 150 to 200 g, a MFR (190/21.6) ranging from 10 to 15 g/10min, a haze ranging from 70 to 80%, and a clarity ranging from 8 to 15%,such values being essentially a function of the film thickness.

Such values of mechanical strength and transparency are consideredunacceptable, particularly in food packaging applications. In theattempt of improving the transparency, low density polyethylene (LDPE)prepared by high-pressure polymerization, which is known for beingtransparent, has been added to the medium density polyethylene preparedby means of chromium catalysts. In the present description and in thefollowing claims, the term LDPE is used to indicate a polyethylenehaving a density from 0.910 to 0.930 g/cm³.

For example, an LDPE film having a density of 0.930 g/cm³ and a MFR(190/2.16) of 1 g/10 min may have a clarity of above 99% at a thicknessof 50 μm.

Although the compositions made of MDPE and LDPE show an increasedtransparency, for example in terms of a certain increase of clarity upfrom an initial value of about 13% (MDPE alone) to a final value 56%(MDPE added with LDPE) at a thickness of 50 μm, a first disadvantage ofthese compositions is that such increase of transparency is stillinsufficient for film applications in food industry. A seconddisadvantage is that such a relative increase of transparency isobtained at the expenses of the mechanical strength. In particular, forexample, MDPE films having a dart drop impact of 180 g, when added withLDPE, may have a dart drop impact in the range of 130-165 g depending onthe amount of LDPE added to MDPE. Such worsening of the mechanicalproperties of the mixture is deemed to depend on the intrinsic poormechanical dart drop impact of the LDPE.

Thus, no significant improvement in transparency has been attained byadding a LDPE to a MDPE prepared by means of a chromium catalyst and therelative improvement of the transparency inevitably results in anunacceptable worsening of the mechanical properties of the film.

It is also known to use a blend of a metallocene-catalyzed mediumdensity polyethylene (mMDPE) with low density polyethylene (LDPE) and/ora linear low density polyethylene (LLDPE), to produce blown films, asfor example described by patent U.S. Pat. No. 6,114,456. Compositions ofsuch kind have sufficient processability and are used to make blownfilms which have to some extent the good optical properties of LDPE andthe good mechanical properties of mMDPE. However, such compositions havethe main disadvantage in that the dart drop impact sensibly decreases asthe density increases.

Patent application WO 01/62847 discloses a bimodal extrusion compositionof polyethylene which is prepared by (co)polymerizing ethylene in amultistage polymerization sequence of successive polymerization stagesin the presence of a single site catalyst. According to WO 01/62847, thebimodal composition of polyethylene can be extruded with addition ofsmall amounts, namely 10 wt-% or less, of high pressure LPDE by blendingor by coextrusion. The addition of LDPE to such a bimodal composition,however, does not allow to obtain a film product having adequate opticalproperties.

A polyethylene film made from a composition of a high-densitypolyethylene (HDPE) and a low-density polyethylene (LDPE) prepared byhigh-pressure polymerization process is also known and has been hithertoused as a packaging material utilizing its transparency. However, themechanical strength of the polyethylene film is yet insufficient.Therefore, there have been attempts to improve the impact resistancethereof. In order to improve the impact resistance, U.S. Pat. No.6,426,384 for example teaches to prepare a polyethylene film forpackaging starting from a polyethylene resin composition comprising alinear low-density polyethylene prepared using a metallocene-basedcatalyst and a high-density polyethylene prepared using a Ziegler typecatalyst. However, the increase of the impact resistance is stillinsufficient.

EP-A1-1 470 185 describes a blend from about 20% by weight to about 80%by weight of a high-molecular weight, medium density polyethylene havinga multimodal molecular weight distribution and about 20% by weight toabout 80% by weight of a linear low density polyethylene. The mediumdensity polyethylene is prepared by using Ziegler catalysts. The blendmay optionally contain a third polymer, such as for example low densitypolyethylene, in an amount preferably less than 50% by weight of thetotal blend. However, the dart drop impact and the tear strength of thefilms prepared starting from such blend are inadequate.

SUMMARY OF THE INVENTION

In view of the above, the Applicant has perceived the need of providinga polyethylene composition, as well as a process for the preparationthereof and a film comprising such a polyethylene composition which, insharp contrast to the prior art, although having a density which mayrange in the medium-high density range, has a high dart drop impact anda high transparency, while maintaining a good degree of processabilityso as to permit to use low working temperatures.

In other words, the technical problem underlying the present inventionis that of providing a polyethylene composition having a suitableprocessability, while simultaneously achieving an improved balancebetween both mechanical and optical properties, in particular in termsof impact resistance and clarity. Such problem, as discussed above, isparticularly felt in the medium-high density range film applications.

According to a first aspect of the present invention, theabove-mentioned technical problem is solved by a polyethylenecomposition comprising:

a) from 50 to 89% by weight of a first polyethylene component comprisingat least one multimodal ethylene polymer including a plurality ofethylene polymer fractions having distinct molecular weights andcomonomer contents, at least one of said plurality of ethylene polymerfractions being prepared by the use of a single site catalyst; and

b) from 50 to 11% by weight of a second polyethylene componentcomprising a low or medium density polyethylene.

In the present description and in the following claims, the expression“single site catalyst” is used to indicate any transition metalcoordination compound comprising at least one ligand, such as forexample a compound selected in the group of cyclopentadienylderivatives, phenoxyimin derivatives, as well as neutral or chargedbidentate or tridentate nitrogen ligands with 2 or 3 coordinatingnitrogen atoms.

In the present description and in the following claims, the expression“low or medium density polyethylene” is used to indicate anypolyethylene having a density in the range 0.910 to 0.940 g/cm³.

For the purpose of the present description and of the claims whichfollow, except where otherwise indicated, all numbers expressingamounts, quantities, percentages, and so forth, are to be understood asbeing modified in all instances by the term “about”. Also, all rangesinclude any combination of the maximum and minimum points disclosed andinclude any intermediate ranges therein, which may or may not bespecifically enumerated herein.

Thanks to the fact that the first polyethylene component includes aplurality of ethylene polymer fractions having distinct molecularweights, i.e. thanks to the fact that the first polyethylene compositionis multimodal, the composition of the invention, on the one side, mayhave a broad molecular distribution, which advantageously permits toimprove the processing of the composition. Furthermore, thanks to thefact that the multimodal first polyethylene component of the inventionincludes a plurality of ethylene polymer fractions having distinctcomonomer contents, the composition of the invention, on the other side,may be tailored in such a way to preferentially include relativelygreater amounts of comonomer within the relatively higher molecularweight fractions, and relatively smaller amounts of comonomer within therelatively lower molecular weight fractions, which advantageouslypermits to improve the mechanical properties of the composition, and inparticular the puncture resistance as well as the tensile and tearstrength of the film products prepared therefrom.

Furthermore, thanks to the presence of a second polyethylene componentcomprising a polyethylene having a density ranging in the low and mediumdensity range, the composition of the invention has, in addition to theabove-mentioned suitable processability and mechanical properties, alsoimproved optical properties, in particular in terms of clarity andgloss.

Surprisingly, such improvement of the optical properties does notsubstantially affect the mechanical and processability properties of thecomposition of the invention. So, the present invention advantageouslyallows to obtain a balance between optical and mechanical properties,which are normally conflicting with each other.

If the second polyethylene component is present in an amount lower than11%, the transparency of the polyethylene composition is inadequate,while if the second polyethylene component is present in an amounthigher than 50%, an unacceptable worsening of the mechanical propertiesis observed.

Preferably, the polyethylene composition comprises from 55 to 85% byweight of said first polyethylene component and from 45 to 15% by weightof said second polyethylene component. More preferably, the polyethylenecomposition comprises from 60 to 85% by weight of said firstpolyethylene component and from 40 to 15% by weight of said secondpolyethylene component. Still more preferably, the polyethylenecomposition comprises from 60 to 80% by weight of said firstpolyethylene component and from 40 to 20% by weight of said secondpolyethylene component.

Within such preferred composition ranges, it is advantageously possibleto prepare films having a further improved combination of optical andmechanical properties, while being at the same time easily processable.

In order to obtain films having a particularly advantageous combinationof mechanical and optical properties, a preferred embodiment of thecomposition of the invention provides a polyethylene compositioncomprising from 70 to 80% by weight of said first polyethylene componentand from 30 to 20% by weight of said second polyethylene component.

The first polyethylene component has preferably a density of from 0.920to 0.970 g/cm³, more preferably of from 0.920 to 0.960 g/cm³, still morepreferably of from 0.930 to 0.950 g/cm³ and, in particular, of from0.932 to 0.945 g/cm³.

The above-mentioned advantageous effects of the invention in terms ofimproved processing, mechanical resistance and optical properties areparticularly pronounced when the density of the multimodal firstpolyethylene component ranges in the medium-high density range, e.g. inthe range from 0.932 to 0.945 g/cm³.

Preferably, the polyethylene composition has a density of from 0.915 to0.965 g/cm³, more preferably from 0.915 to 0.960 g/cm³, still morepreferably from 0.915 to 0.955 g/cm³, particularly preferably from 0.915to 0.945 g/cm³. According to further preferred embodiments of theinvention, the polyethylene composition has preferably a density of from0.920 to 0.955 g/cm³, more preferably from 0.930 to 0.950 g/cm³ and,still more preferably, from 0.935 to 0.940 g/cm³. A further improvementof the optical properties without a substantial affection of themechanical properties and an increase in the stiffness is advantageouslyachieved when the density falls in these preferred ranges. In otherwords, an improved balance between optical and mechanical properties isadvantageously obtained.

Preferably, at least one fraction of the above-mentioned plurality ofethylene polymer fractions of the first polyethylene component comprisesan ethylene copolymer containing a comonomer including at least one1-olefin.

Preferably, the at least one 1-olefin has formula R¹CH═CH₂, wherein R¹is hydrogen or an alkyl radical with 1 to 12 carbon atoms and, morepreferably, wherein R¹ is an alkyl radical with 1 to 10 carbon atoms.

In the above-mentioned ethylene copolymer, in addition to ethylene it ispossible to use any 1-olefin having from 3 to 12, preferably to 3 to 10,carbon atoms, e.g. propene,1-butene,1-pentene, 1-hexene,4-methyl-1-pentene, 1-heptene, 1-octene and 1-decene. More particularly,the ethylene copolymer preferably comprises 1-olefins having from 4 to 8carbon atoms, e.g. 1-butene, 1-pentene, 1-hexene, 4-methylpentene or1-octene, in copolymerized form as comonomer unit. Particular preferenceis given to 1-olefins selected from the group consisting of 1-butene,1-hexene and 1-octene.

The above-mentioned comonomers can be present either individually or ina mixture with one another.

According to a preferred embodiment of the polyethylene composition ofthe invention, the first polyethylene component comprises a multimodalpolyethylene in which the lower molecular weight ethylene polymers arepreferably homopolymers or, alternatively, copolymers containing lessthan 1% by weight of comonomer(s), more preferably less than 0.5%, whilethe higher molecular weight ethylene polymers are preferably copolymerscontaining a predetermined amount of comonomer(s) which is preferablygreater than 1% by weight. Preferably, such predetermined amount ofcomonomer(s) of the copolymers either increases as a function of themolecular weight of the higher molecular weight ethylene polymers orremains equal, the amount of comonomer(s) of the highest molecularweight ethylene polymer being of 2-10% by weight based on the copolymer.

Preferably, the first polyethylene component comprises a bimodalpolyethylene including a relatively low molecular weight ethylenepolymer and a relatively high molecular weight ethylene polymer.Preferably, the bimodal polyethylene has a density comprised in therange from 0.932 to 0.945 g/cm³, more preferably from 0.930-0.940 g/cm³.

Preferably, the relatively low molecular weight component and therelatively high molecular weight component of the bimodal firstpolyethylene composition have an intrinsic viscosity in decalin at 135°of from 0.6 to 1.2 dl/g and, respectively, of from 2.5 to 5 dl/g asdetermined according to EN ISO 1628-3:2003.

In this way, the balance between optical and mechanical properties ofthe polyethylene composition of the invention is further improved.

More preferably, the composition of the invention comprises, as a firstpolyethylene component, a bimodal polyethylene component including arelatively low molecular weight component having a MFR (190/21.6) offrom above 5 to 100 g/10 min and a relatively high molecular weightcomponent having a MFR (190/21.6) of from 5 to 15 g/10 min, and in anycase lower than the MFR (190/21.6) of the relatively low molecularweight component.

According to a preferred embodiment of the polyethylene composition ofthe invention, the first polyethylene component comprises a bimodalpolyethylene, in which said relatively low molecular weight ethylenepolymer is preferably a homopolymer or, alternatively, a copolymercontaining less than 1% by weight of comonomer, more preferably lessthan 0.5%, while said relatively high molecular weight ethylene polymeris preferably a copolymer containing a predetermined amount of comonomerpreferably higher than 1%, for example comprised between 1% and 10% byweight, preferably from 2 to 8%, more preferably from 2.5 to 5% and,still more preferably, from 3 to 4% by weight.

In this way, and in particular thanks to the absence of comonomer or, atthe most, thanks to a limited content of comonomer in the relatively lowmolecular weight fraction of the first polyethylene, content which, assaid above, is preferably not higher than 1% and more preferably nothigher than 0.5%, the composition of the invention is particularlyeasily processable, which advantageously allows to use lower workingtemperatures, for example in the range of 180-250° C. Preferably, therelatively high molecular weight ethylene copolymer comprises from 1% to10% by weight, preferably from 2 to 8%, more preferably from 2.5 to 5%and, still more preferably, from 3 to 4% by weight of a comonomer, whichpreferably includes at least one of the comonomers described above, inparticular a comonomer selected from the group of propene, 1-butene,1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and1-decene.

According to a preferred embodiment of the invention, at least theethylene polymer fraction of the multimodal (e.g. bimodal) polyethyleneof the first polyethylene component having the lowest molecular weightis prepared by means of the above-mentioned single site catalyst.

Preferably, the above-mentioned single site catalyst used to prepare theat least one ethylene polymer fraction of the multimodal polyethylene ofthe first polyethylene component is a metallocene.

So, for example, in the preferred embodiment according to which thefirst polyethylene component comprises a bimodal polyethylene includingtwo ethylene polymer fractions having distinct molecular weights andcomonomer contents, namely a relatively high molecular weight ethylenepolymer fraction preferably including copolymers containing apredetermined amount of comonomer preferably greater than 1% by weight,and a relatively low molecular weight ethylene polymer fractionpreferably including homopolymers or copolymers containing less than 1%by weight of comonomer, more preferably less than 0.5%, the relativelyhigh molecular weight ethylene polymer fraction is preferably obtainedby means of the above-mentioned single site catalyst, for example bymeans of a metallocene.

According to a preferred embodiment of the invention, a mixed typecatalyst may be used, i.e. a catalyst comprising particles eachcontaining a plurality of different kind of active species, in which atleast one active specie is a single site catalyst.

Thanks to the fact that in the case of a mixed type catalyst containingat least two active species at least two different polymerizationcatalysts are provided within the same catalyst system, on the one sidethe first polyethylene compound is multimodal and, on the other side, itis advantageously possible to prepare the first polyethylene componentby means of a polymerization process carried out in a single reactor.

When the mixed type catalyst contains only two active species, forexample, a bimodal first polyethylene component of the composition maybe advantageously obtained, which permits, on the one side, to prepare abroad molecular weight distribution composition and, on the other side,to polymerize both the relatively low molecular weight component and therelatively high molecular weight component in a parallel way, i.e.substantially in a simultaneous manner, in one single reactor.

By way of illustrative example, the mixed catalyst may contain at leastone metallocene (by way of illustrative and not limiting example, ahafnocene or a zirconocene) component and one iron component. Inparticular, the mixed catalyst may contain one metallocene (e.g.hafnocene or zirconocene) component and one iron component.

However, any other combination of active species which are able topolymerize ethylene in such a manner as to obtain a relatively highmolecular weight component containing preferably at least 1% ofcomonomer and, respectively, a relatively low molecular weight componentcontaining an amount of comonomer preferably lower than 1%, isacceptable for the purpose of the invention.

Preferably, in the preferred embodiment in which the catalyst containsone metallocene, for example a hafnocene or a zirconocene, component andone iron component, the iron component has preferably a tridentateligand bearing at least two aryl radicals, each bearing a halogen oralkyl substituent in the ortho-position(s) as described by formula (B)disclosed in W02005/103095 in the name of the Applicant, which is herebyincorporated by reference.

The mixed catalyst may for example comprise, as active species, at leastone first component and at least one second component, as well as atleast one activating compound so as to advantageously improve thepolymerization activity of the first and second component. Theactivation of the at least one first component and of the at leastsecond component of the catalyst may be effected using the sameactivating compound or different activating compounds. The molar ratioof the first component to the activating compound, as well as the molarratio of the second component to the activating compound, may range in afirst and, respectively, in a second predetermined range which, withreference to the illustrative example of the catalyst comprising onemetallocene component and one iron component, is preferably as follows.The molar ratio of the metallocene component to the activating compoundmay range from 1:0.1 to 1:10000, preferably from 1:1 to 1:2000. Themolar ratio of the iron component to the activating compound is alsousually in the range from 1:0.1 to 1:10000, preferably from 1:1 to1:2000.

Suitable activating compounds which are able to react with one of thecomponents of the mixed catalyst, for example with the hafnocenecomponent or the iron component, to convert the same into acatalytically active or more active compound are, for example, compoundssuch as an aluminoxane, a strong uncharged Lewis acid, an ionic compoundhaving a Lewis-acid cation or an ionic compound containing a Brönstedacid as cation.

The catalyst may further comprise at least one support. The preferredcatalyst composition according to the invention comprises one support ora plurality of supports, which may be organic or inorganic. The firstcomponent and/or the second component and the optional activatingcompound of the catalyst, in particular, may be supported, for exampleon different supports or together on a common support.

Preferably a finely divided organic or inorganic solid support, such asfor example silica, hydrotalcite, magnesium chloride, talc,montmorillonite, mica, or an inorganic oxide or a finely divided polymerpowder (e.g. polyolefin or a polymer having polar functional groups) isused. The catalyst system may further comprise a metal compound,preferably a metal of group 1, 2 or 13 of the Periodic Table andpreferably different from the above-mentioned activating component,which is used as constituent of the catalyst for the polymerization orcopolymerization of olefins, for example to prepare a catalyst solidcomprising the support and/or be added during or shortly before thepolymerization.

It is also possible for the catalyst system firstly to be prepolymerizedwith a α-olefin, preferably with a linear C₂-C₁₀-1-alkene and inparticular ethylene or propylene. The resulting prepolymerized catalystsolid may then be submitted to the actual polymerization step.

Furthermore, a small amount of an olefin, preferably an α-olefin, forexample vinylcyclohexane, styrene or phenyldimethylvinylsilane can beadded as additive during or after the preparation of the catalyst. Otheradditives, such as for example wax or oil, can be also added during orafter the preparation of the catalyst.

Preferably, the first polyethylene component of the polyethylenecomposition has a molar mass distribution width M_(w)/M_(n) of from 5 to30. Preferably, the first polyethylene component has a weight averagemolar mass M_(w) of from 50 000 g/mol to 500 000 g/mol. Preferably, thefirst polyethylene component has a z-average molecular weight M_(z) ofless than 1 Mio. g/mol.

Preferably, the first polyethylene component of the polyethylenecomposition has a molar mass distribution width M_(w)/M_(n) in the rangefrom 6 to 20 and, more preferably, from 7 to 15.

Preferably, the weight average molar mass M_(w) of the firstpolyethylene component of the polyethylene composition is in the rangefrom 100 000 g/mol to 300 000 g/mol and, more preferably, from 120 000g/mol to 250 000 g/mol.

The z-average molar mass M_(z) of the first polyethylene component ofthe polyethylene composition is preferably in the range of from 250 000g/mol to 700 000 g/mol and, more preferably, from 300 000 g/mol to 500000 g/mol. The definition of z-average molar mass M_(z) is used herewithin accordance with the definition given in High Polymers Vol. XX, Raffund Doak, Interscience Publishers, John Wiley & Sons, 1965, page 443.

According to a particularly preferred embodiment of the presentinvention, the first polyethylene component has the following preferredfeatures:

-   -   a molar mass distribution width M_(w)/M_(n) of from 5 to 30;    -   a weight average molar mass M_(w) of from 50000 g/mol to 500 000        g/mol; and    -   a z-average molecular weight M_(z) of less than 1 Mio. g/mol.

Such a preferred combination of features advantageously permits toprovide a polyethylene composition in which the first polyethylenecomponent has improved and balanced processability and mechanicalproperties, which in turn advantageously permits to add sensibly greatamounts of the second polyethylene component, for example in the rangeof 35-50% by weight, with advantageous increase of the transparencywithout substantially altering the processing and mechanical properties.

The first polyethylene component of the polyethylene composition has aMFR (190/21.6) which is preferably in the range of from 5 to 100 g/10min, more preferably in the range of from 7 to 60 g/10 min and, stillmore preferably, of from 9 to 50 g/10 min.

In the present description and in the following claims, the MFR(190/21.6) is the melt flow rate measured in accordance with ISO 1133,condition G, namely at 190° C. and under a load of 21.6 kg.

The first polyethylene component preferably comprises a fraction havinga molar mass of below 1 Mio. g/mol as determined by Gel PermeationChromatography (GPC) in the standard determination of the molecularweight distribution according to standard DIN 55672 with1,2,4-trichlorobenzene at 140° C. More preferably, said fraction amountsto at least 95.5% by weight of the first polyethylene component.

The first polyethylene component has preferably a Eta(vis)/Eta(GPC)lower than 0.95, Eta(vis) being the intrinsic viscosity as determinedaccording to ISO 1628-1 and -3 and Eta(GPC) being the viscosity asdetermined by GPC according to DIN 55672, with 1,2,4-Trichlorobenzene,at 140° C.

According to a preferred embodiment of the composition of the invention,the second polyethylene component has a density of from 0.910 to 0.940g/cm³, preferably of from 0.910 to 0.933 g/cm³, more preferably of from0.915 to 0.933 g/cm³ and, still more preferably, of from 0.925 to 0.930g/cm³.

Preferably, the second polyethylene component has a density lower thanthe density of the first polyethylene component.

The second polyethylene component of the composition of the inventionhas preferably a MFR (190/2.16) of from 0.2 to 50 g/10 min, morepreferably from 0.3 to 10 g/10 min, and, still more preferably, from 0.3to 5 g/10 min.

According to a second aspect thereof, the present invention relates to aprocess for producing a polyethylene composition, comprising the stepsof:

a) preparing a multimodal first polyethylene component by:

a1) providing at least one single site catalyst;

a2) subjecting ethylene, optionally with at least one comonomer, in thepresence of said at least one single site catalyst, to a plurality ofpolymerization stages intended to obtain a respective plurality ofethylene polymer fractions;

a3) distinguishing said plurality of ethylene polymer fractions withrespect to each other on the basis of molecular weights and comonomercontents;

b) preparing a second polyethylene component comprising a low or mediumdensity polyethylene;

c) adding said second polyethylene component to said multimodal firstpolyethylene component so prepared so as to obtain a compositioncomprising from 50 to 89% by weight of the first polyethylene componentand from 50 to 11% by weight of the second polyethylene component.

Thanks to the fact that the first polyethylene component is of themultimodal type and that the second polyethylene component comprises alow density polyethylene or a medium density polyethylene, it isadvantageously possible to obtain a polyethylene composition which iseasily processable and has improved optical properties. The addition—inthe above-mentioned predetermined amount—of a second polyethylenecomponent including a LDPE or a MDPE to a multimodal first polyethylenecomponent defined as above, advantageously allows to prepare apolyethylene composition having simultaneously an improvement of theoptical properties, in particular in terms of haze, clarity and gloss,without substantially compromising the mechanical properties, inparticular in terms of dart drop impact, as well as the processabilityof the composition. An improved balance among conflicting properties istherefore achieved, and this improvement is particularly pronounced whenthe density of the multimodal first polyethylene component ranges in themedium-high density range.

The step of providing at least one single site catalyst is preferablycarried out in such a manner to obtain a catalyst according to any oneof the preferred embodiments described above with reference to thecomposition of the invention. So, for example, if the catalyst is amixed type catalyst, it is advantageously possible to prepare themultimodal first polyethylene component by means of a polymerizationprocess carried out in a single reactor.

Said step of preparing the multimodal first polyethylene component iscarried out in such a manner as to obtain a first polyethylene componenthaving a density of from 0.920 to 0.955 g/cm³, more preferably from0.930 to 0.950 g/cm³ and, still more preferably, from 0.932 to 0.945g/cm³.

Ethylene with at least one comonomer, and optionally preferably withhydrogen as preferred molar mass regulator, is subjected, in thepresence of said at least one single site catalyst, to a plurality ofpolymerization stages, preferably to a two polymerization stages so asto conveniently obtain a relatively low molecular weight component and arelatively high molecular weight component.

Preferably, the process is carried out so as to obtain a relatively lowmolecular weight component and a relatively high molecular weightcomponent having an intrinsic viscosity in decalin at 135° C. of from0.6 to 1.2 dl/g and, respectively, of from 2.5 to 5 dl/g as determinedaccording to EN ISO 1628-3:2003.

In this way, the processability of the composition is further improved.

Preferably, the process is carried out so as to obtain a bimodal firstpolyethylene component comprising a relatively low molecular weightcomponent having a MFR (190/21.6) of from above 5 to 100 g/10 min and arelatively high molecular weight component having a MFR (190/21.6) offrom 5 to 15 g/10 min, and in any case lower than the MFR (190/21.6) ofthe relatively low molecular weight component

According to a preferred embodiment of the process of the invention, theethylene may be copolymerized with at least one 1-olefin, such as forexample one or more of the 1-olefins described above with reference tothe preferred embodiments of the composition of the invention. So, forexample, the ethylene is preferably subjected to copolymerization withat least one 1-olefin having formula R¹CH═CH₂, wherein R¹ is hydrogen oran alkyl radical with 1 to 12 carbon atoms and, more preferably, with 1to 10 carbon atoms. As a comonomer, any 1-olefin having from 3 to 12carbon atoms, e.g. propene, 1-butene, 1-pentene, 1-hexene,4-methyl1-pentene, 1-heptene, 1-octene and 1-decene may be used. Thecomonomer preferably comprises 1-olefins having from 4 to 8 carbonatoms, e.g. 1-butene, 1-pentene, 1-hexene, 4methylpentene or 1-octene,in copolymerized form as comonomer unit. Particular preference is givento 1-olefins selected from the group consisting of 1-butene, 1-hexeneand 1-octene.

The above-mentioned comonomers can be present either individually or ina mixture with one another.

Preferably, the temperature at which ethylene is (co)polymerized iscarried out is of from 20 to 200° C. Preferably, the pressure at whichethylene is (co)polymerized is carried out is from 0.05 to 1 MPa.

The step of preparing the multimodal first polyethylene is preferablycarried out in such a way as to obtain a first polyethylene componenthaving:

-   -   a molar mass distribution width M_(w)/M_(n) of from 5 to 30;    -   a weight average molar mass M_(w) of from 50000 g/mol to 500 000        g/mol; and    -   a z-average molecular weight M_(z) of less than 1 Mio. g/mol.

Preferably, the step of distinguishing the plurality of ethylene polymerfractions with respect to each other on the basis of molecular weightsis carried out by using at least two active catalytic species.

More preferably, such at least two active catalytic species, of which atleast one is of the single site type, are incorporated in the samecatalyst particle. In such a preferred embodiment, a correspondingplurality of polymerization stages is advantageously carried out in asubstantially simultaneous manner in a parallel mode and the result ofsuch plurality of substantially simultaneous polymerization stages is amultimodal polyethylene composition. Thanks to these preferred features,it is advantageously possible to prepare the first polyethylenecomponent by means of a single step polymerization process in a singlereactor, thus advantageously reducing both the plant costs and theenergy consumption with respect to the processes carried out in aplurality of reactors.

Alternatively, the above-mentioned at least two active catalytic speciesare incorporated in different catalyst particles. Also in this case, byproviding a mixture of at least two particulate catalysts, acorresponding plurality of polymerization stages is advantageouslycarried out in a substantially simultaneous manner in a parallel modeand the result of the different substantially simultaneouspolymerization stages is a multimodal polyethylene composition.

The step of distinguishing the plurality of ethylene polymer fractionswith respect to each other on the basis of molecular weights may be alsocarried out by polymerizing ethylene in a respective plurality ofreactors arranged in series with each other. In this case, acorresponding plurality of polymerization stages is advantageouslycarried out in a serial mode, and the result of the different subsequentpolymerization stages is a multimodal polyethylene composition. Thanksto these preferred steps, it is advantageously possible to prepare thefirst polyethylene component by means of a multistage polymerizationprocess in which the polymerization stages are subsequent to each other.

Independently of the number of reactors used, with each of these threealternative methods, good mixing of the polyethylene is advantageouslyachieved and the control of the molecular weight fractions of thevarious polymers and of the molecular weight distributions isconveniently simple.

A further possible alternative in order to distinguish the plurality ofethylene polymer fractions with respect to each other on the basis ofmolecular weights is that of blending a plurality of polymer fractionseach obtained by the use of a respective catalyst. In this case, byblending such a plurality of polymer fractions, it is advantageouslypossible to obtain a multimodal polyethylene composition in a parallelmode, as a result of the blending of polymer fractions which have beenseparately prepared, either simultaneously or subsequently to eachother, by the use of respective catalyst in respective polymerizationstages.

The above-mentioned addition step is preferably carried out so as toobtain a composition comprising from 50 to 89% by weight of said firstpolyethylene component and from 50 to 11% by weight of said secondpolyethylene component, more preferably from 55 to 85% by weight of saidfirst polyethylene component and from 45 to 15% by weight of said secondpolyethylene component, still more preferably the polyethylenecomposition comprises from 60 to 85% by weight of said firstpolyethylene component and from 40 to 15% by weight of said secondpolyethylene component and, in particular.

Within such preferred composition ranges, it is advantageously possibleto prepare films having a further improved transparency.

In order to obtain films having a particularly advantageous combinationof mechanical and optical properties, a preferred embodiment of theprocess of the invention provides an additional step which is carriedout so as to prepare a polyethylene composition comprising from 65 to80% by weight of said first polyethylene component and from 35 to 20% byweight of said second polyethylene component and, more preferably, from70 to 80% by weight of said first polyethylene component and from 30 to20% by weight of said second polyethylene component

According to a preferred embodiment of the process of the invention, theabove-mentioned step of adding the second polyethylene component to thefirst polyethylene component is carried out by blending.

In this way, a good mixing of the first polyethylene component and ofthe second polyethylene component is advantageously achieved.

Alternatively, the step of adding the second polyethylene component tothe first polyethylene component is carried out by compounding or bycoextrusion.

The polymerization of ethylene in order to prepare the firstpolyethylene component can be carried out using all industrially knownpolymerization methods at temperatures in the range from 60° C. to 350°C., preferably from 0 to 200° C. and particularly preferably from 25 to150° C., and under pressures of from 0.5 to 4000 bar, preferably from 1to 100 bar, and particularly preferably from 3 to 40 bar. Thepolymerizations effected to prepare the first polyethylene component canbe carried out in a known manner in bulk, in suspension, in the gasphase or in a supercritical medium in the conventional reactors used forthe polymerization of olefins. It can be carried out batchwise or, morepreferably, continuously in one stage (for example, as described above,if a mixed catalyst is used) or in more stages. Solution processes,suspension processes, stirred gas-phase processes and gas-phasefluidized-bed processes are all possible. The second polyethylenecomponent is preferably prepared by conventional high-pressurepolymerization processes in tube reactors or autoclaves.

The mean residence times are preferably from 0.5 to 5 hours. Theadvantageous pressure and temperature ranges for carrying out thepolymerizations usually depend on the polymerization method.

In the case of suspension polymerizations, for example, thepolymerization is usually carried out in a suspension medium, preferablyan inert hydrocarbon such as isobutane or mixtures of hydrocarbons orelse in the monomers themselves. The polymerization temperatures aregenerally in the range from −20° C. to 115° C., and the pressure isgenerally in the range from 1 to 100 bar. The solids content of thesuspension is generally in the range from 10% to 80%. The polymerizationcan be carried out either batchwise or continuously, e.g. in stirringautoclaves, in tube reactors, such as for example in loop reactors.Particular preference is given to employing the Phillips PF process asdescribed in US-A U.S. Pat. No. 3,242,150 and US-A U.S. Pat. No.3,248,179. The gas-phase polymerization is generally carried out in therange from 30 to 125° C. at pressures of from 1 to 50 bar.

In the case of high-pressure polymerization processes, which areconventionally carried out at pressures of from 1000 to 4000 bar, inparticular from 2000 to 3500 bar, high polymerization temperatures aregenerally also set. Advantageous temperature ranges for thesehigh-pressure polymerization processes are from 200° C. to 320° C., inparticular from 220° C. to 290° C. In the case of low-pressurepolymerization processes, it is usual to set a temperature which is atleast a few degrees below the softening temperature of the polymer. Inparticular, temperatures of from 140° C. to 310° C. are preferably setin these polymerization processes.

Among the above-mentioned polymerization processes used to prepare thefirst polyethylene component, particular preference is given togas-phase polymerization and, more in particular, in gas-phasefluidized-bed reactors, solution polymerization and suspensionpolymerization, such as for example in loop reactors and stirred tankreactors. The gas-phase polymerization may also be carried out in thecondensed or supercondensed mode, in which part of the circulating gasis cooled to below the dew point and is recirculated as a two-phasemixture to the reactor. Furthermore, it is possible to use a multizonereactor in which at least two reciprocally linked polymerization zonesare provided, so that the polymer is passed alternately through these atleast two zones a predetermined number of times. The at least two zonesmay also be subjected to different polymerization conditions. Such amultizone reactor is described, for example, in WO 97/04015. Thedifferent or identical polymerization stages, as already explainedabove, may also, if desired, be carried out in a serial manner, namelyin a plurality of reactors arranged in series to each other so as toform a polymerization cascade. A parallel reactor arrangement using twoor more identical or different processes is also possible. Furthermore,molar mass regulators, such as for example hydrogen, or conventionaladditives, such as for example antistatics, may also be used in thepolymerizations. If hydrogen is added and if the temperature isincreased, a lower z-average molar mass is advantageously achieved.

The polymerization is preferably carried out in a single reactor, inparticular in a gas-phase reactor. The polyethylene powder so obtainedis advantageously more homogeneous with respect to the polyethyleneobtained as a result of a cascade process, where a number ofpolymerization stages are carried out in a serial manner in a pluralityof reactors arranged in series to each other, so that, unlike the powderobtainable by means of the cascade process, a possible subsequentextrusion is conveniently not necessary in order to obtain a homogeneousproduct.

The composition of the invention may also be prepared by blending afirst polyethylene component and a second polyethylene component asdefined above, preferable by intimate mixing of individual components,for example by melt extrusion in an extruder or kneader (as described,for example, in “Polymer Blends” in Ullmann's Encyclopedia of IndustrialChemistry, 6^(th) Edition, 1998, Electronic Release).

According to a further aspect thereof, the present invention relates tothe use of a polyethylene composition as defined above for producing afilm.

Furthermore, the present invention relates to a film comprising apolyethylene composition as defined above, as well as to a particularlypreferred film selected from the group of stretch films, hygienic films,films for office uses, sealing layers, automatic packaging films,composite and laminating films.

Films in which the polyethylene of the invention is present as asignificant component are ones which contain from 50 to 100% by weight,preferably from 60 to 90% by weight, of the polyethylene of theinvention, based on the total polymer material used for manufacture. Inparticular, films including a plurality of layers in which in which atleast one of the layers contains from 50 to 100% by weight of thepolyethylene of the invention are also included.

In general the films are preferably produced by plastification of thepolyethylene composition of the invention at a melt temperature in therange of from 190 to 230° C., by forcing the plasticized polyethylenethrough an annular die and cooling. The film may further comprise offrom 0 to 30% by weight, preferably 0.1 to 3 by weight of auxiliariesand/or additives known per se, e.g. processing stabilizers, stabilizersagainst the effects of light and heat, customary additives such aslubricants, antioxidants, antiblocking agents and antistatics, and also,if appropriate, dyes.

The polyethylene composition of the invention may be used to preparefilms with a thickness of from 5 μm to 2.5 mm. The films can for examplebe prepared via blown film extrusion with a thickness of from 5 μm to250 μm or via flat film extrusion, such as cast film extrusion with athickness of from 10 μm to 2.5 mm. During blown film extrusion thepolyethylene melt is forced through an annular die. The bubble which isformed is inflated with air and hauled off at a higher speed than thedie outlet speed. The bubble is intensively cooled by a current of airso that the temperature at the frost line is lower than the crystallitemelting point. The bubble is then collapsed, trimmed if necessary androlled up using a suitable winding instrument. The polyethylenecomposition of the invention may be extruded either according to twoalternative configurations known in the art, namely according to a “longstalk” configuration or according to a “conventional” configurationdepending on the density of the polyethylene. In the “long stalk”configuration, which is normally suitable for blowing high densitypolyethylene, the bubble of polymer blown into a film has a well definedand longer neck height with respect to the “conventional” configuration,which is suitable in blowing low density polyethylene.

The films may be obtained for example in chill roll lines orthermoforming film lines. Furthermore composite films essentially basedone the polyethylene composition of the invention may be produced oncoating and laminating lines. Especially preferred are composite filmswherein paper, aluminum or fabric substrates are incorporated into thecomposite structure. The films may have a single layer or a plurality oflayers, each obtained by coextrusion.

The polyethylene composition of the invention is suitable for producingfilms in blown film and cast film plants at high outputs. The filmsdisplay improved mechanical properties, in particular, as betterdescribed in the following, high tensile strength and tear strengthtogether with improved optical properties, in particular transparencyand gloss. The composition of the invention is suitable, in particular,for preparing packaging films, such as for example heat sealing films,also for heavy duty sacks and in particular for films intended to beused in the food industry.

The films of the invention are especially suitable in applicationsrequiring high clarity and gloss such as carrier bags to permit highquality printing, laminating films in foodstuff applications, since thefilms of the invention also have a very low odor and taste level andautomatic packaging films, since the film can be processed on high-speedlines.

The films of the invention having a thickness in the order of 50 μm haveadvantageously a haze, as determined by ASTM D 1003-00 on a BYK GardenerHaze Guard Plus Device on at least 5 pieces of film of size 10×10 cm,below 22%. The dart drop impact of films having a thickness in the orderof 50 μm as determined by ASTM D 1709 Method A is advantageously above140 g. The clarity of films having a thickness in the order of 50 μm asdetermined by ASTM D 1746-03 on a BYK Gardener Haze Guard Plus Device,calibrated with calibration cell 77.5, on at least 5 pieces of 10×10 cmfilms is advantageously at least 86%. The 20° gloss of films having athickness in the order of 50 μm as determined by ASTM D 2457-03 on a 20°gloss meter with a vacuum plate for fixing the film, on at least 5pieces of film, is advantageously of at least 15.

The scrap obtained during the production of these films can beconveniently recycled. If the films are produced by a first extruder,film trimmings may be compacted or ground and fed to a second extruder,where they are melted so as to be ready to be fed back to the mainextruder and, in this way, conveniently recycled. The film trimmingsshould be reground to grains having a size which can be fed into thefeed section of the first extruder together with the virginpolyethylene. The films containing such recycled material do not showany significant deterioration of the properties compared to filmswithout recycled material.

The polyethylene composition of the invention may be also used toprepare articles by means of a number of techniques, such as for exampleblow molding, injection molding, roto-molding and compression molding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be further described by means of thefollowing preferred embodiments without restricting the scope of theinvention.

Example 1 (Invention)

a) Preparation of the Individual Components

0.90 kg of 2,6-diacetylpyridine (99%), 2, 56 kg of phosphorus pentoxide(P₂O ₅), and a solution of 2.14 kg of 2,4-dichloro-6-methylaniline(100%) were solubilized in 20 l of tetrahydrofuran. The mixture wasstirred for 15 min and then heated under reflux for 18 hours at 70° C.After completion of the reaction, the obtained suspension was cooled to20° C., stirred for 30 min and then filtered and washed with 6 l oftetrahydrofuran. The filtrate, having a volume of 26 l, was concentratedunder vacuum (250 mm Hg, 55° C.). The volume was reduced by rotaryevaporation up to a final concentrate of 3.5 l. 20 l of methanol wereadded so as to obtain crystallization. The resulting suspension (23.5 l)was filtered and washed with 6 l of methanol, thus resulting in a volumeof 27 l. The humid product (1.38 kg) resulting from the filtration wasset under drying condition in free air for one night. This gave a firstfraction of 1.36 kg of2,6-Bis[1-(2,4,6-trimethylphenylimino)ethyl]pyridine in 51% yield. Thefiltrate (27 l) was concentrated as described above up to a finalconcentrate of 2.5 kg. 4 1 of methanol were added. The resultingsuspension was agitated for 1 hour at room temperature and washed with0.4 l of methanol. A second fraction of 50 g was in this way obtained.Thus, a total of 1400 g of2,6-Bis[1-(2,4,6-trimethylphenylimino)ethyl]pyridine in 53% yield wereobtained. A reaction with iron(II) dichloride was carried out asdescribed by Qian et al., Organometallics 2003, 22, 4312-4321.

b) Support Pretreatment

140 kg Sylopol 2107, a spray-dried silica gel from Grace, was calcinatedat 600° C. for 6 hours.

c) Preparation of the Mixed Catalyst System

A mixture of 509 g (0.84 mol) of2,6-Bis[1-(2,4-dichloro-6-methylphenylimino)ethyl]pyridine iron(II)dichloride, prepared according to the above-mentioned procedure undera), 4131 g (8.4 mol) of bis(n-butylcyclopentadienyl)hafnium dichloride,commercially available from Crompton, and 195 l of MAO (4.75 M intoluene, 926 mol) was stirred at 20° C. for 2 h and after cooling to 0°C. subsequently added while stirring to 140 kg of the pretreated supportmaterial b). The solution was added with a flow rate lower than 100kg/h. The obtained product was stirred for further 30 minutes and heatedto 40° C. The solid was dried under reduced pressure until it wasfree-flowing. After sieving, 320 kg of catalyst were obtained (residualsolvent: 41%).

(d) Polymerization

The polymerization was carried out in a fluidized-bed reactor having adiameter of 3.7 m in the presence of the mixed catalyst described above.The reaction temperature was 105° C., the pressure in the reactor was 25bar, the reaction gas had the following composition: 49 vol % ethylene,5.1 vol % hexane, 0.6 vol % hexene, 45 vol % nitrogen, 1.5 kg/htrihexylaluminum (2 wt % in hexane). The output was 5.5 t/h.

The MDPE polyethylene so obtained had a density of 0.939 g/cm³ and a MFR(190/21.6) of 28 g/10 min. The MDPE, conveniently added with 700 ppm ofa conventional processing additive, namely Polybatch® AMF 705 (availablefrom A. Schulman) was used as a first polyethylene component, whose mainproperties are shown in Table 1 below, while Lupolen 3220 F, which is aLDPE commercially available from Basell Polyolefine GmbH having adensity of 0.930 g/cm³, and a MFR (190/2.16) of 0.9 g/10 min, was usedas a second polyethylene component in an amount of 11% by weight.

Examples 2-4 (Invention)

In Examples 2-4 a first and a second polyethylene components as thosedescribed in Example 1 were used, except for the amount of LDPE, whichwas set to 20%, 30% and, respectively, 40% by weight.

TABLE 1 First PE component of Examples 1-4 Density [g/cm³] 0.939 MFR(190/21.6) [g/10 min] 28 Eta(vis)/Eta(GPC) 2.08 M_(w) [g/mol] 140000M_(w)/M_(n) 14.4 M_(z) 462000 GPC % at molar mass 1 Mio 99.3 —HC═CH₂ [1/1000C] 1.51 total-CH₃ [ 1/1000C] 8.0

Where

-   -   density is the polymer density    -   MFR (190/21.6) is the melt flow rate according to standard ISO        1133, condition G    -   Eta(vis) is the intrinsic viscosity as determined according to        ISO 1628-1 and    -   Eta(GPC) is the viscosity as determined by GPC according to DIN        55672, with 1,2,4-Trichlorobenzene, at 140° C.    -   M_(w) is the weight average molar mass;    -   M_(n) is the number average molar mass    -   M_(z) is the z-average molar mass    -   GPC % at molar mass 1 Mio is the % by weight according to gel        permeation chromatography below a molar mass of 1 Mio g/mol.        -   HC═CH₂ is the amount of vinyl groups        -   total-CH₃ is the amount of CH3-groups per 1000 C including            end groups.

Example 5-8 (Comparative)

Innovex LL6910AA, which is a conventional LLDPE prepared by the use of aZiegler-Natta catalyst commercially available from BP (density equal to0.936 g/cm³, MFR (190/2.16) of 1.0 g/10 min), conveniently added with700 ppm Polybatch® AMF 705, was used as a first polyethylene component,whose properties are shown in Table 2, while Lupolen 3220 F was used asa second polyethylene component in an amount of 11%, 20%, 30% and,respectively, 40% by weight.

TABLE 2 First PE component of Examples 5-8 Density [g/cm³] 0.936 MFR(190/2.16) [g/10 min] 1.0

Where

-   -   MFR (190/2.16) is the melt flow rate according to standard ISO        1133, condition D.

Examples 9-12 (Comparative)

Lupolen 3721 C, which is a MDPE prepared by the use of a chromiumcatalyst commercially available from Basell (density equal to 0.937g/cm³, MFR (190/21.6) of 12.5 g/10 min), was used as a firstpolyethylene component, whose properties are shown in Table 3, whileLupolen 3220 F was used as a second polyethylene component.

TABLE 3 First PE component of Examples 9-12 Density [g/cm³] 0.937 MFR(190/21.6) [g/10 min] 12.5 Eta(vis)/Eta(GPC) 2.80 M_(w) [g/mol] 240000M_(w)/M_(n) 12.1 M_(z) 1650000 GPC % at molar mass 1 Mio 95.8 —HC═CH₂ [1/1000C] 0.72 total-CH₃ [ 1/1000C] 5.4

Granulation and Film Extrusion

The polyethylene compositions of Example 1-12 were homogenized andgranulated on a ZSK 30 (Werner Pfleiderer) with screw combination 8A.The processing temperature was 220° C., the screw speed 250/min, theoutput of 20 kg/h.

Each polyethylene composition of the Examples above was extruded intofilms by blown film extrusion on a Weber film extruder equipped with acollapsing device with wooden flatted boards.

The diameter of the ring die was 50 mm, the gap width was 2/50 and theangle along which the cooling air is blown onto the extruded film was45° . No filters were used. The 25D Extruder with a screw diameter of 30mm and a screw speed of 50 turns per min gave an output of 5.1 kg/h. Theblow-up ratio was 1:2 and the haul-off speed 4.9 m/10 min. The height ofthe frost line was 160 mm. Films with a thickness in the order of 50 μmwere obtained. The specific thickness of each film, as well as theprocessing properties and optical and mechanical properties of thedifferent films, are summarized in Tables 4 and 5.

TABLE 4 processing and optical properties of the films Thickness GlossGloss Haze Clarity Example [μm] 20° 60° [%] [%] 1 51 14 63 22 86 2 50 3383 16 92 3 51 54 99 14 97 4 51 66 104 12 98 5 50 63 97 14 99 6 51 77 10613 99 7 51 75 105 12 98. 8 52 71 102 11 99 9 51 1.5 16 61 23 10 51 2.222 45 33 11 51 3.2 29 34 47 12 50 4.2 35 30 56

TABLE 5 mechanical properties of the films Dynamic Tensile Tearpropagation Dart Test strength (Elmendorf method) Drop [Nm/mm] [N/mm²][mN] Example [g] W_(s) W_(tot) MD TD MD TD 1 276 11.6 13.1 42.2 35.12323 6058 2 241 11.1 12.5 41.8 34.5 2323 14848 3 235 9.8 12.1 40.0 32.62072 16387 4 190 8.2 10.8 38.2 32.5 1754 15539 5 119 6.2 9.6 44.5 45.61605 8602 6 120 4.7 8.6 41.7 41.7 1185 8319 7 120 4.15 8.7 42.3 39.11142 10045 8 117 4.2 8.5 40.3 36.8 1079 8884 9 165 3.0 8.1 — — 443 1654410 146 2.8 8.2 — — 426 17674 11 144 2.9 8.7 — — 266 16450 12 133 3.2 8.8— — 370 14723

The values presented in the description and in the Tables weredetermined in the following way.

NMR samples were placed in tubes under inert gas and, if appropriate,melted. The solvent signals served as internal standard in the ¹H- and¹³C-NMR spectra and their chemical shift was converted into the valuesrelative to TMS.

The degree of branching in the individual polymer fractions wasdetermined by the method of Holtrup (W. Holtrup, Makromol Chem. 178,2335 (1977)) coupled with ¹³C-NMR.

The density [g/cm³] was determined in accordance with ISO1183.

The determination of the values M_(n), M_(w), M_(z) and of the molarmass distribution M_(w)/M_(n) derived therefrom was carried out by meansof high-temperature gel permeation chromatography on a WATERS 150 Cusing a method based on DIN 55672 and the following columns connected inseries: 3× SHODEX AT 806 MS, 1× SHODEX UT 807 and 1× SHODEX AT-G underthe following conditions: solvent: 1,2,4-trichlorobenzene (stabilizedwith 0.025% by weight of 2,6-di-tert-butyl-4-methylphenol), flow: 1ml/min, 500 μl injection volume, temperature: 140° C. The columns werecalibrated with polyethylene standards with molar masses of from 100 bis10⁷ g/mol. The evaluation was carried out by using the Win-GPC softwareof Fa. HS-Entwicklungsgesellschaft für wissenschaftliche Hard-undSoftware mbH, Ober-Hilbersheim.

For the purposes of the present invention, the expression MFR(190/21.6), known also as “high load melt flow rate”, has beendetermined at 190° C. under a load of 21.6 kg in accordance with ISO1133, condition G.

For the purposes of the present invention, the expression MFR (190/2.16)has been determined at 190° C. under a load of 2.16 kg in accordancewith ISO 1133, condition D.

In order to determine the reflection properties of the films, glossmeasurements were carried out according to ISO 2813 on a reflectometerat impingement angles of 20° and 60°, on at least 5 pieces of film witha thickness of 50 μm.

The haze was determined by ASTM D 1003-00 on a BYK Gardener Haze GuardPlus Device on at least 5 pieces of film 10×10 cm with a thickness of 50μm.

The clarity was determined by ASTM D 1746-03 on a BYK Gardener HazeGuard Plus Device, calibrated with calibration cell 77.5, on at least 5pieces of film 10×10 cm with a thickness of 50 μm.

In order to determine the puncture resistance of films under shockloading, the dart drop was determined by ASTM D 1709, Method A on 10film samples having a thickness of 50 μm.

In order to determine the strength of the films under dynamic loading,dynamic tests were carried out according to DIN 53373, so as to obtainthe fracture energy W_(s) up to the first tear and the total fractureenergy W_(tot) for the penetration.

The tensile strength test was performed according to ISO 527 both inmachine direction (MD) and at right angle to the machine direction,known as transverse direction (TD)

The tear propagation test, otherwise known as Elmendorf method, wasperformed according to ISO 6383/2.

1-10. (canceled)
 11. A polyethylene composition comprising: (a) from 50to 89% by weight of a first polyethylene component comprising amultimodal polyethylene including a plurality of ethylene polymerfractions having distinct molecular weights and co-monomer contents, atleast one of said plurality of ethylene polymer fractions being preparedby the use of a single site catalyst; and (b) from 50 to 11% by weightof a second polyethylene component comprising a low density polyethyleneor a medium density polyethylene.
 12. The polyethylene composition ofclaim 11 having a density of 0.915 to 0.955 g/cm³.
 13. The polyethylenecomposition of claim 11, wherein said first polyethylene component has adensity of from 0.920 to 0.960 g/cm³.
 14. The polyethylene compositionof claim 11, wherein said second polyethylene component has a density offrom 0.910 to 0.940 g/cm³.
 15. The polyethylene composition of claim 11,wherein the first polyethylene component comprises a bimodalpolyethylene including a low molecular weight ethylene homopolymer and ahigh molecular weight ethylene copolymer.
 16. The polyethylenecomposition of claim 15 having a density of 0.915 to 0.955 g/cm³. 17.The polyethylene composition of claim 15, wherein said firstpolyethylene component has a density of from 0.920 to 0.960 g/cm³. 18.The polyethylene composition of claim 15, wherein said second componenthas a density of from 0.910 to 0.940 g/cm³.
 19. The polyethylenecomposition of claim 15, wherein said high molecular weight ethylenecopolymer comprises 1 to 10% by weight of a comonomer selected from thegroup consisting of propene, 1-butene, 1-pentene, 1-hexene,4-methyl-1-pentene, 1-heptene, 1-octene and 1-decene, and mixturesthereof.
 20. A process for producing a polyethylene composition, saidprocess comprising: (a) subjecting ethylene, optionally withcomonomer(s), to a plurality of polymerization stages, wherein at leastone of the plurality of polymerization stages is carried out in thepresence of a single site catalyst to prepare a multimodal firstpolyethylene component; (b) preparing a second polyethylene componentcomprising a low density polyethylene or a medium density polyethylene;and (c) combining said second polyethylene component and said multimodalfirst polyethylene component to obtain a polyethylene compositioncomprising from 50 to 89% by weight of the first polyethylene componentand from 50 to 11% by weight of the second polyethylene component. 21.The process of claim 20, wherein the single site catalyst comprise ametallocene.
 22. The process of claim 20, wherein the polyethylenecomposition has a density of 0.915 to 0.955 g/cm³.
 23. The process ofclaim 20, wherein said first polyethylene component has a density offrom 0.920 to 0.960 g/cm³.
 24. The process of claim 20, wherein saidsecond component has a density of from 0.910 to 0.940 g/cm³.
 25. Theprocess of claim 20, wherein the first polyethylene component comprisesa bimodal polyethylene including a low molecular weight ethylenehomopolymer and a high molecular weight ethylene copolymer.
 26. A filmcomprising a polyethylene composition of claim
 11. 27. The film of claim26, wherein the polyethylene composition has a density of 0.915 to 0.955g/cm³.
 28. The film of claim 26, wherein said first polyethylenecomponent has a density of from 0.920 to 0.960 g/cm³.
 29. The film ofclaim 26, wherein said second component has a density of from 0.910 to0.940 g/cm³.
 30. The film of claim 26, wherein the first polyethylenecomponent comprises a bimodal polyethylene including a low molecularweight ethylene homopolymer and a high molecular weight ethylenecopolymer.